Cooking utensil

ABSTRACT

Cooking utensil suitable for heating on both thermal and induction heat sources, comprising a container having a container bottom to which a base is connected, the base comprising a peripheral wall and a bottom side and having a layered structure. An inner region of the bottom side of the base is at least partly constructed in a material of higher thermal conductivity than the material of an outer region of the bottom side of the base. The layered structure is constructed such that the average thermal conductivity of the layered structure between the inner region of the bottom side of the base and a peripheral region of the container bottom is higher than the average thermal conductivity of the layered structure between the inner region of the bottom side of the base and a central region of the container bottom.

The present invention relates to a cooking utensil according to thepreamble of the first claim.

A cooking utensil is for example known from U.S. Pat. No. 4,350,259. Thecooking utensil known from U.S. Pat. No. 4,350,259 is suitable forheating on both thermal and induction heat sources. The cooking utensilcomprises a container to the bottom of which a base is connected. Thisbase has a layered structure comprising an upper conductive layerconnected to the bottom of the container, an inductive layer connectedto the upper conductive layer, a lower conductive layer connected to theinductive layer and a protective layer connected to the lower conductivelayer. The conductive layers make the cooking utensil suitable for useon thermal heat sources and the inductive layer makes it suitable foruse on induction heat sources.

In a first embodiment described in U.S. Pat. No. 4,350,259, theinductive layer of the base of the cooking utensil, which is interposedbetween the upper and lower conductive layers, is provided withopenings. The purpose of these openings is to allow the material of theupper and lower conductive layers to fill these openings duringconstruction of the cooking utensil, so that the upper and lowerconductive layers contact each other and that the mechanical anchoringof the inductive layer in between the conductive layers can be improved.

In a second embodiment described in U.S. Pat. No. 4,350,259, theprotective layer of the base of the cooking utensil, which is applied onthe lower conductive layer, is provided with openings. These openingsare provided in order to allow the material of the lower conductivelayer to fill these openings during construction of the cooking utensil,so that the protective layer is anchored in the lower conductive layer.

The cooking utensil known from U.S. Pat. No. 4,350,259 however has thedisadvantage that, upon heating the cooking utensil on a thermal heatsource, such as for example a gas oven or a ceramic hob, the bottom ofthe container is heated unevenly. More particularly, the bottom of thecontainer is heated more quickly in the centre than at its periphery. Asa result, the temperature of the centre of the bottom of the containermay become too high, so that food being prepared in the container may beburnt at the centre.

It is an aim of the present invention to provide a cooking utensil ofwhich the base enables a more even heating of the bottom of thecontainer.

This aim is achieved according to the invention with a cooking utensilshowing the technical characteristics of the characterising part of thefirst claim.

In the cooking utensil of the invention, the bottom side of the base,which is provided to contact the heat source, comprises an inner regionand an outer region. The inner region is at least partly constructed ina material of higher thermal conductivity than the material of the outerregion. As a result, when the cooking utensil is used on a thermal heatsource, heat is absorbed by the base faster at the inner region than atthe outer region of the bottom side of the base. The layered structureof the base is further constructed such that its average thermalconductivity is higher between the inner region of the bottom side andthe peripheral region of the container bottom than between the innerregion of the bottom side and the central region of the containerbottom. As a result, when the cooking utensil is used on a thermal heatsource, heat is conducted faster from the inner region of the bottomside to the peripheral region of the container bottom than to thecentral region of the container bottom.

An analysis of the problem of uneven heating has shown that it is mainlycaused by the fact that in most commonly used thermal heat sources, suchas for example a ceramic hob, more heat is generated more towards thecentre than towards the periphery of the heat source. In other words,there is a heat excess in the centre with respect to the periphery ofthe heat source. By providing the higher thermal conductivity of thelayered structure towards the periphery than towards the centre of thecontainer bottom, this central heat excess may be distributed by thebase over the whole of the container bottom in a faster manner. As aresult, a more uniform heating of the container bottom can be achievedand burning of food at the centre of the container bottom can beprevented.

Furthermore, by providing the bottom side of the base with an innerregion at least partly in a material of higher thermal conductivity, thecentral excess of heat is partly removed from the heat source, so thatthe difference in temperature between the centre and the periphery ofthe heat source can be decreased. As a result, the heat source can havea more uniformly distributed temperature, so that the overall uniformityof heating of the container bottom can be further enhanced.

The higher thermal conductivity in the inner region on the bottom sidealso has the effect that the base of the cooking utensil of theinvention absorbs heat faster in the region of the heat source where themost heat is generated. As a result, the amount of time needed forheating the container bottom can be reduced, so that the preparation offood with the cooking utensil of the invention can sooner be startedwith.

In a preferred embodiment of the cooking utensil of the invention, thelayered structure of the base comprises an upper conductive layerconnected to the container bottom, an inductive layer connected to theupper conductive layer, a lower conductive layer connected to theinductive layer and a protective layer connected to the lower conductivelayer. The upper and lower conductive layers have a higher thermalconductivity than the inductive layer and the protective layer. Theinductive layer has good induction properties and is as such providedfor enabling heating on induction heat sources. The conductive layershave good thermal conduction properties for distributing the heatgenerated by thermal heat sources or in the inductive layer in case ofuse on an induction heat source.

In this preferred embodiment, at least the outer region of the bottomside of the base is formed by the protective layer. This means that theprotective layer forms the whole of the outer region of the bottom side,but that it may also comprise a portion within the inner region of thebottom side of the base. According to the invention, the inner region isat least partly in a material which has a higher thermal conductivitythan the material of the outer region. So the fact that in thisembodiment the whole of the outer region is formed by the protectivelayer means that the inner region of the bottom side is at least partlyof a material with a thermal conductivity above that of the protectivelayer. This material can be that of the lower conductive layer or of anadditional layer, as will become apparent from further embodiments ofthe cooking utensil of the invention described below.

Further, in this preferred embodiment, the thermal conductivity of thelayered structure of the base at the level of the inductive layer ishigher at the peripheral wall than inwardly from the peripheral wall.This is a way of constructing the layered structure such that theaverage thermal conductivity of the layered structure is higher towardsthe peripheral region than towards the central region of the containerbottom.

Constructing the layered structure such that the thermal conductivity atthe level of the inductive layer is higher at the peripheral wall can beachieved in many ways. Preferably, this construction is achieved in thatthe upper and lower conductive layers of the base contact each other atthe peripheral wall of the base and that the inductive layer separatesthe upper and lower conductive layers inwardly from the peripheral wall.This means that the upper and lower conductive layers contact each otheronly at the peripheral wall and not inwardly from the peripheral wall.As the inductive layer has a lower thermal conductivity than theconductive layers, the thermal conductivity of the layered structure ishigher at the peripheral wall by the contact between the conductivelayers.

The higher conductivity at the peripheral wall can however also beachieved in other ways, for example by providing cut-outs in theinductive layer at the peripheral wall in which the material of theconductive layers is allowed to penetrate during construction of thecooking utensil, or by reducing the thickness of the inductive layer atthe peripheral wall. In the first embodiment of the prior art cookingutensil described above, the inductive layer is provided with openingswhich are filled by the material of the conductive layers duringconstruction. These openings are provided in order to improve themechanical anchoring of the inductive layer between the conductivelayers. The openings are however distributed over the whole of theinductive layer and it is not specified that these openings create avariation in the thermal conductivity of the layered structure. As aresult, there is no teaching in U.S. Pat. No. 4,350,259 of how toprovide the layered structure with a higher thermal conductivity at theperipheral wall of the base, nor that this can be used to achieve a moreuniform heating of the container bottom.

In a further preferred embodiment of the cooking utensil of theinvention, the protective layer forms part of the inner region, one ormore cut-outs being provided in the protective layer in the innerregion. This means that, where the cut-outs are provided, the materialof the inner region is that of the lower conductive layer. Additionally,a layer of highly conductive material may be applied in any of thecut-outs, so that, the material of the inner region at the cut-outs isthat of this additional layer. The highly conductive material has athermal conductivity equal to or above that of the lower conductivelayer. In either case, whether or not the additional layer is applied inthe cut-outs, it is achieved that the material in the inner region atthe cut-outs has a higher thermal conductivity than the material of theouter region of the bottom side of the base. In the second embodiment ofthe prior art cooking utensil described above, the protective layer ofthe base of the cooking utensil is provided with openings which arefilled by the material of the lower conductive layer during constructionof the cooking utensil. These openings are provided in order tomechanically anchor the protective layer in the lower inductive layer.The openings are however distributed over the whole of the protectivelayer and it is not specified that these openings create a variation inthe thermal conductivity of the bottom side of the base. As a result,there is no teaching in U.S. Pat. No. 4,350,259 of how to provide thebottom side of the base with an inner region at least partly of higherconductivity than an outer region, nor that this can be used to achievea more uniform heating of the container bottom.

The one or more cut-outs can have various shapes. In one preferredembodiment of the cooking utensil of the invention, the protective layeris provided with a cut-out which is located centrally on the bottom sideof the base and has a diameter of about one third of the diameter of thebase. Preferably, a layer of highly conductive material is applied inthis central cut-out. The highly conductive material has a thermalconductivity which is equal to or above the thermal conductivity of thelower conductive layer. This layer of highly conductive material forms athermal bridge between the thermal heat source and the lower conductivelayer, so that the speed of heat absorption of the inner region of thebase can be further increased.

In other preferred embodiments of the cooking utensil of the invention,the cut-outs take the shape of one or more rings or illustrations. Thesering-shaped and illustration-shaped cut-outs may be combined with eachother as well as with the central cut-out described above. Thesecut-outs may also be provided with a layer of highly conductivematerial. The highly conductive material is preferably copper or acopper alloy, but may also be any other material with high thermalconductivity known to the person skilled in the art.

The protective layer of the base preferably comprises a peripheralportion which forms substantially half of the peripheral wall of thebase. In this way, half of the peripheral wall of the base is protectedagainst corrosion, while the other half is left uncovered, so that asideways thermal expansion of the layers of the base as a result ofheating is substantially not obstructed. As a result, the base can beconstructed with a substantially flat bottom side, whereas a concavityin the bottom side of the base is required in most prior art cookingutensils of similar type to enable vertical thermal expansion of thebase without the bottom side becoming convex. By leaving part of theperipheral wall of the base uncovered, the provision of such concavityis no longer required or at least the amount of concavity can bereduced, as the layers can freely expand sideways. In this way, when thecooking utensil of the invention is for example used on a ceramic hob,substantially the whole of the bottom side of the base is immediately incontact with the ceramic hob, so that the speed of heat absorption ofthe base and in particular its inner region can be further increased.

The invention will be further elucidated by means of the followingdescription and the appended figures.

FIG. 1 shows a bottom view of a first preferred embodiment of thecooking utensil according to the invention.

FIG. 2 shows a side and cross-sectional view of the cooking utensil ofFIG. 1, the cross section being taken along line II-II of FIG. 1.

FIG. 3 shows a bottom view of a second preferred embodiment of thecooking utensil according to the invention.

FIG. 4 shows a side and cross-sectional view of the cooking utensil ofFIG. 3, the cross section being taken along line IV-IV of FIG. 3.

FIG. 5 shows a bottom view of a third preferred embodiment of thecooking utensil according to the invention.

FIG. 6 shows a side and cross-sectional view of the cooking utensil ofFIG. 5, the cross section being taken along line VI-VI of FIG. 5.

The first embodiment of the cooking utensil according to the invention,shown in FIGS. 1 and 2, comprises a container 1 with a bottom 2. A base3 having a layered structure is connected to the bottom 2 of thecontainer 1. The base 3 comprises a peripheral wall 10 and a bottom side9, which is located opposite the container bottom 2 and is provided tocontact the heat source. The bottom side 9 of the base 3 comprises anouter region 9 a, which is delimited by the peripheral wall 10, and aninner region 9 b inwardly from the outer region 9 a. The containerbottom 2 comprises a peripheral region 2 a at the peripheral wall 10 anda central region 2 b inwardly from the peripheral region 2 a.

The inner region 9 b of the bottom side 9 of the base 3 is at leastpartly constructed in a material of higher thermal conductivity than thematerial of the outer region 9 a of the bottom side 9 of the base 3. Asa result, when the cooking utensil is used on a thermal heat source,heat is absorbed by the base 3 faster at the inner region 9 b than atthe outer region 9 a of the bottom side 9 of the base 3. Furthermore, acentral excess of heat generated in a thermal heat source is partlyremoved from the heat source, so that the difference in temperaturebetween the centre and the periphery of the heat source can bedecreased. As a result, the heat source can have a more uniformlydistributed temperature, so that a more uniform heating of the containerbottom 2 can be achieved. The higher thermal conductivity in the innerregion 9 b on the bottom side 9 also has the effect that the base 3 ofthe cooking utensil of the invention absorbs heat faster in the regionof the heat source where the most heat is generated. As a result, theamount of time needed for heating the container bottom 2 can be reduced,so that the preparation of food can sooner be started with.

The layered structure of the base 3 is further constructed such that theaverage thermal conductivity of the layered structure between the innerregion 9 b of the bottom side 9 of the base 3 and the peripheral region2 a of the container bottom 2 is higher than the average thermalconductivity of the layered structure between the inner region 9 b ofthe bottom side 9 of the base 3 and the central region 2 b of thecontainer bottom 2. As a result, when the cooking utensil is used on athermal heat source, heat is conducted faster from the inner region 9 bof the bottom side 9 to the peripheral region 2 a of the containerbottom 2 than to the central region 2 b of the container bottom 2. As aresult, a central heat excess generated by a thermal heat source may bedistributed by the base 3 over the whole of the container bottom 2 in afaster manner. This can lead to a more uniform heating of the containerbottom 2, so that burning of food at the centre of the container bottom2 can be prevented.

The layered structure of the base 3 comprises, as shown from top tobottom in the cross section of FIG. 2: an upper conductive layer 4, aninductive layer 5, a lower conductive layer 6 and a protective layer 7.The protective layer 7 forms at least the outer region 9 a. Theprotective layer 7 may also form the outer region 9 a only, but as shownit is preferred that the protective layer 7 also forms part of the innerregion 9 b of the bottom side 9. This is preferred as where theprotective layer 7 is applied, the material of the base 3 is protectedagainst corrosion. Furthermore, the protective layer 7 improves theappearance of the cooking utensil towards the user.

The upper and lower conductive layers 4, 6 have good thermal conductionproperties for distributing the heat generated by thermal heat sourcesor in the inductive layer 5 in case of use on an induction heat source.The upper and lower conductive layers 4, 6 are constructed in a materialhaving a higher thermal conductivity than the inductive layer 5 and theprotective layer 7. The inductive layer 5 is constructed in a materialhaving good inductivity properties, so that the cooking utensil issuitable for use on induction heat sources.

The upper and lower conductive layers 4, 6 are preferably constructed inaluminium, an aluminium alloy, copper or a copper alloy. The upper andlower layers 4, 6 may however also be constructed in any other materialof good thermal conductivity known to the person skilled in the art. Theinductive layer 5 is for example constructed in the known “430” steelalloy, or any other material of good inductivity properties. Theprotective layer 7 is constructed in a substantially corrosion-freematerial, such as for example the known “430” steel alloy, or any other.

The upper and lower conductive layers 4, 6 preferably have substantiallythe same thickness, but they may also have a different thickness. Theinductive layer 5 preferably has a thickness of about one third of thethickness of the conductive layers 4, 6. The protective layer ispreferably as thin as mechanically possible. Suitable thicknesses areabout 3 mm for the upper and lower conductive layers 4, 6, about 1 mmfor the inductive layer 5 and about 0.5 mm for the protective layer 7.

The cooking utensil of the invention preferably has a circular shape,but may also have an oval, square or any other shape.

The base 3 of the cooking utensil is preferably connected to the bottom2 of the container by subsequently placing the different layers 4-7 onthe bottom 2, heating the layers 4-7 and applying a high pressure on thelayers 4-7. In this way, a layered structure with strong intermetallicbonding is achieved.

The thermal conductivity of the layered structure of the base 3 at thelevel of the inductive layer 5 is higher at the peripheral wall 10 thaninwardly from the peripheral wall 10. In the three embodiments of thecooking utensil of the invention, shown in FIGS. 1-6, this is achievedin that the upper and lower conductive layers 4, 6 contact each other atthe peripheral wall 10, but only at the peripheral wall 10: inwardlythey are separated by the inductive layer 5. By this peripheral contact,it is achieved that heat absorbed by the lower conductive layer 6 istransferred more quickly from the lower conductive layer 6 to the upperconductive layer 4 at the periphery 10 than at the centre of the base 3.The higher conductivity at the peripheral wall 10 can however also beachieved in other ways (not shown), for example by providing cut-outs inthe inductive layer 5 at the peripheral wall 10 in which the material ofthe conductive layers 4, 6 is allowed to penetrate during constructionof the cooking utensil, or by reducing the thickness of the inductivelayer 5 at the peripheral wall, or in other ways.

The upper and lower conductive layers 4, 6 are preferably constructed inthe same material, so as to improve their interconnection at theperipheral wall 10, but may also be constructed in different materials.

According to the invention, the inner region 9 b of the bottom side 9 ofthe base 3 is at least partly constructed in a material of higherthermal conductivity than the material of the outer region 9 a of thebottom side 9 of the base 3. In all the embodiments shown, the outerregion 9 a and part of the inner region 9 b is formed by the protectivelayer 7. In order to achieve that the inner region 9 b is at leastpartly constructed in a material of higher thermal conductivity thanthat of the protective layer 7, a number of cut-outs 11-13 are providedin the protective layer 7 in the inner region 9 b. At these cut-outs11-13, the material of the bottom side 9 is that of the lower conductivelayer 6 or that of an applied additional layer 8 (cf. FIGS. 1 and 2) ina material of high thermal conductivity, above that of the protectivelayer 7 and preferably equal to or above that of the lower conductivelayer 6.

In the first embodiment of FIGS. 1 and 2, a first cut-out 11 is locatedcentrally of the bottom side 9 of the base and has a diameter of aboutone third of the diameter of the base. A plate 8 in the material of highthermal conductivity is applied in this first cut-out 11. A series ofsecond cut-outs 12 are provided in the protective layer 7 in the innerregion 9 b, between the central cut-out 11 and the outer region 9 a.These second cut-outs 12 have the shape of an illustration. On FIG. 1,it is shown that the material of the lower conductive layer 6 is visiblethrough these second cut-outs 12.

The highly conductive material of the plate 8 is preferably copper or acopper alloy, but may also be any other material of high thermalconductivity known to the person skilled in the art.

The second embodiment of the cooking utensil according to the invention,shown in FIGS. 3 and 4, differs from the first embodiment of FIGS. 1 and2 in that the protective layer 7 does not have a central cut-out 7 witha highly conductive plate 8. Instead, the central portion 15 of theprotective layer 7 is formed as a recess in the bottom side 9 of thebase 3. This central recess 15 can increase the stability of the cookingutensil when placed on a flat surface, e.g. a hob of a thermal orinduction oven.

The third embodiment of the cooking utensil according to the invention,shown in FIGS. 5 and 6, differs from the second embodiment of FIGS. 3and 4 in that the illustration-shaped second cut-outs 12 are replaced bya pair of third cut-outs 13, which have the form of concentric rings.Again, these ring-shaped cut-outs 13 providing parts of higher thermalconductivity in the inner region 9 b of the bottom side 9 of the base.

From the above it is clear that the one or more cut-outs 11-13 in theprotective layer 7 can have various shapes. They are preferably achievedby removing part of the protective layer 7 in a milling operation, butmay also be achieved in other ways. The layer 8 in a material of highthermal conductivity can be applied in any of the cut-outs 11-13.

As the cut-outs 11-13 provide portions of higher thermal conductivity,heat is more easily absorbed at the cut-outs 11-13 with respect to theportions which are covered by the protective layer 7. As the cut-outs11-13 are located in the inner region 9 b, they are located where themost heat is initially generated in most commonly used thermal heatsources. In this way, the presence of the cut-outs 11, 12 can stronglyincrease the heat absorption speed of the base 3. By providing the plate8 in highly conductive material, the heat absorption speed can befurther increased, as this plate 8 forms a thermal bridge between thelower conductive layer 6 and the thermal heat source.

As the cut-outs 11-13 are located in the inner region 9 b, the distancefrom the cut-outs 11-13 to the peripheral region 2 a of the containerbottom 2 is longer than the distance to the central region 2 b of thecontainer bottom 2. As a result, it would normally take longer to heatthe peripheral region 2 a than the central region 2 b of the bottom 2 ona thermal heat source. However, because of the peripheral contactbetween the upper and lower conductive layers 4, 6 and the inwardseparation between them by the inductive layer 5 of lower conductivity,the heat absorbed at the cut-outs 11, 12 is transferred to the peripheryand the centre of the bottom 2 in about the same amount of time. As aresult, in the cooking utensil shown in FIGS. 1 and 2, the bottom 2 ofthe container can be heated substantially evenly on a thermal heatsource.

In the three embodiments described above (cf. FIGS. 2, 4 and 6), theprotective layer 7 preferably comprises a peripheral portion 14 whichforms substantially half of the periphery 10 of the base 3. By thisperipheral portion 14, the connection between the protective layer 7 andthe lower conductive layer 6 can be improved. By leaving part of theperipheral wall 10 open, providing the bottom side 9 of the base 3 witha concavity for allowing thermal expansion can be avoided, as the base 3is allowed to expand sideways. As a result, the bottom side 9 can besubstantially flat, so that the contact with for example a ceramic hobis improved and the time lapse at the start can be reduced before thecontainer 2 bottom is heated sufficiently for the preparation of food.

1. Cooking utensil suitable for heating on both thermal and inductionheat sources, comprising a container having a container bottom to whicha base is connected, the base comprising a peripheral wall and a bottomside and having a layered structure, the bottom side of the base beinglocated opposite the container bottom and being provided to contact theheat source, wherein the container bottom comprises a peripheral regionat the peripheral wall and a central region inwardly from the peripheralregion, wherein the layered structure of the base comprises an upperconductive layer connected to the container bottom, an inductive layerconnected to the upper conductive layer, a lower conductive layerconnected to the inductive layer and a protective layer connected to thelower conductive layer, wherein the upper and lower conductive layerscontact each other only at the peripheral wall and are separated fromeach other by the inductive layer inwardly from the peripheral wall, theupper and lower conductive layers having a higher thermal conductivitythan the inductive layer, wherein the bottom side of the base comprisesan outer region delimited by the peripheral wall and an inner regioninwardly from the outer region, the outer region being formed by atleast part of the protective layer and the inner region being at leastpartly constructed of a material of higher thermal conductivity than thematerial of the protective layer such that an average thermalconductivity of the layered structure between the inner region of thebottom side of the base and the peripheral region of the containerbottom is higher than an average thermal conductivity of the layeredstructure between the inner region of the bottom side of the base andthe central region of the container bottom.
 2. Cooking utensil accordingto claim 1, wherein the thermal conductivity of the layered structure atlevel of the inductive layer is higher at the peripheral wall thaninwardly from the peripheral wall.
 3. Cooking utensil according to claim1, wherein the protective layer forms part of the inner region of thebottom side of the base, and including one or more cut-outs in theprotective layer in the inner region.
 4. Cooking utensil according toclaim 3, wherein a first of the one or more cut-outs in the protectivelayer is located centrally on the bottom side of the base, the firstcut-out having a diameter of about one third of a diameter of the base.5. Cooking utensil according to claim 4, wherein a second of the one ormore cut-outs in the protective layer has the form of an illustration.6. Cooking utensil according to claim 5, wherein a third of one or morecut-outs in the protective layer is ring-shaped.
 7. Cooking utensilaccording to claim 3, including an applied layer of a material having athermal conductivity which is equal to or above the thermal conductivityof the lower conductive layer in at least one of the one or morecut-cuts.
 8. Cooking utensil according to claim 7, wherein the appliedlayer is made of copper or a copper alloy.
 9. Cooking utensil accordingto claim 1, wherein the protective layer comprises a peripheral portionwhich forms substantially half of the peripheral wall of the base.